The Angular directive alters the scope, however, the template continues to display the unchanged value

I am working with a directive that looks like this:

.directive('myDirective', function() {
    return {
        restrict: 'AE',
        replace: true,
        templateUrl: '/myDirective.html?v=' + window.buildNumber,
        link: function (scope, element, attrs) {
            scope.itemClasses = attrs.itemClasses || '';
        }
    };
})

Its template is as follows:

<div class="my-directive">
    <div class="items" ng-repeat="item in items">
        <div class="item {{ itemClasses }}">{{ item.title }}</div>
    </div>
</div>

This directive is being called in various places (once per template) like so:

<my-directive item-classes="col-md-6"></my-directive>
...
<my-directive item-classes="col-md-12"></my-directive>

All templates are rendering the same value for itemClasses, despite the link function setting different values (verified using console.log()). However, when I add the attribute scope: true to the directive's code, everything works fine. It appears that having its own inherited scope resolves the issue. Can you please explain this behavior?

Thank you.

Answer №1

When you specify scope: true, a child scope is created for your directive while also inheriting properties from the parent (which I believe is your controller in this case). Each instance of your directive will then have its own distinct scope.

However, when you use scope: false, your directive shares the scope with its parent and does not have its own scope.

So, to address your question about using scope: false: when you write:

scope.itemClasses = attrs.itemClasses || '';

You are essentially assigning the itemClasses property to the parent's scope. This means that although it may appear to work correctly in the link function, in reality you are constantly overwriting the same scope variable in the controller.

Therefore, in your scenario, initially you assign a scope variable to the parent controller:

scope.itemClasses= 'col-md-6';

But subsequently, you overwrite the same scope variable in the parent with a new value:

scope.itemClasses= 'col-md-12';

Does this explanation clarify things for you?

Answer №2

When you bind the item-classes directly from the attributes, you're essentially creating a duplicate of the attribute values.

To address this issue, if you wish to turn input-classes into an input binding, you can use an isolated scope like this:

{
    restrict: 'AE',
    replace: true,
    scope: {
        itemClasses: '='
    },
    templateUrl: '/myDirective.html?v=' + window.buildNumber,
    link: function (scope, element, attrs) {
        // scope.itemClasses = attrs.itemClasses || '';
    }
}

Alternatively, if you prefer not to use isolated scope, you can utilize attrs.$observe:

link: function (scope, element, attrs) {
    attrs.$observe('itemClasses ', function(val) {
        scope.itemClasses = val || '';
    });
}

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